Directory UMM :Data Elmu:jurnal:S:Soil & Tillage Research:Vol52.Issue1-2.Sept1999:
Soil & Tillage Research 52 (1999) 73±81
Crop residue and tillage effects on carbon
sequestration in a Luvisol in central Ohio
S.W. Duiker, R. Lal*
School of Natural Resources, Ohio State University, 2021 Coffey Road,Columbus, OH 43210-1085,USA
Received 3 July 1998; received in revised form 2 March 1999; accepted 1 June 1999
Abstract
Soils play a key role in the global carbon cycle. They can be a source or a sink of carbon and in¯uence CO2 concentrations in
the atmosphere. In order to calculate the carbon budget of a region, the effect of soil management practices on carbon
sequestration in soils needs to be quanti®ed. Objectives of this experiment were to determine: (i) the effects of ridge till, plow
till and no-till on the soil organic carbon (SOC) pool; (ii) the SOC loss or sequestration for mulch rates of 0±
16 Mg haÿ1 yearÿ1 wheat (Triticum aestivum L.) straw applied in combination with each tillage method, and (iii) impacts of
tillage and crop residue treatments on soil physical quality, including aggregation and porosity. The experiment was initiated
in 1989 on a Crosby silt loam (Stagnic Luvisol) in Central Ohio. Seven years after initiation of the experiment, there was a
positive, linear effect of residue application rate on SOC contents in all tillage treatments. In the eighth year of the experiment
these trends were con®rmed for plow and no-till, but not for ridge till. Linear-regression equations, relating SOC content for
the 0±10 cm soil depth to mulch rate, were: for no-till: SOC (Mg haÿ1) 15.21 0.32 [Residue (Mg haÿ1 yearÿ1)] (r 0.68)
and for plow till: SOC 11.95 0.27 [Residue] (p 0.72). The carbon conversion ef®ciencies were 8% per year for plow till
and 10% per year for no-till. Detailed sampling at different depths revealed that increases in SOC content were only signi®cant
for the 0±5 cm depths of plow and no-till treatments. Effects of crop residue application on water stable aggregation in the 0±
10 cm layer were most pronounced with plow till and ridge till but not with no-till. Water retention characteristics, a measure
of pore size distribution, was not in¯uenced by tillage system, but crop residue application had a signi®cant effect on water
retention in the 0±10 cm layer at matric suctions of 30±300 kPa. This means that residue application increased macropores of
diameters 1±10 mm. It is concluded that, depending on the amount of crop residue returned to the soil, the large numbers
of farmers converting from plow to no-till cultivation in the Corn Belt may create an important sink for atmospheric CO2.
# 1999 Elsevier Science B.V. All rights reserved.
Keywords: Soil organic matter; Aggregation; Carbon sequestration; Mulching; Conservation tillage; Greenhouse effect; Soil quality
1. Introduction
*Corresponding author. Tel.: +1-614-292-9069; fax: +1-614292-7432
E-mail address: [email protected] (R. Lal)
Concern with global warming has led to a surge of
interest in evaluating the effect of management practices on carbon sequestration in soils. This interest is
justi®ed because soils play a key role in the global
0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 5 9 - 8
74
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
carbon budget, containing 3.5% of the carbon reserves
of the earth, compared with 1.7% in the atmosphere,
8.9% in fossil fuels, 1.0% in biota and 84.9% in the
oceans (Lal et al., 1995). Land use change is still a
major source of carbon emission due to burning and
decomposition of vegetation and declining soil
organic carbon (SOC) contents in soils. Depending
on management, soils can be an important sink for
carbon. However, realization of the sink capacity of
soils requires adoption of appropriate soil management practices that increase SOC content.
In the U.S., many farmers have shifted from plow
till to conservation tillage systems. The area under
conservation tillage (leaving >30% of crop residue on
the soil surface) has increased from 29 million ha
(26% of planted area) in 1989 to 40 million ha
(35%) in 1994 (Bull and Sandretto, 1996), and is
expected to increase to 75% by the year 2020 (Lal,
1997). The Corn Belt and Northern Plains are the
regions where conservation tillage (especially no-till)
is most popular. In 1994, about 14 million ha of
cropland in the Corn Belt had >30% residue coverage,
while 17 million ha had 0.25 mm and mean
weight diameter (MWD) were calculated according
to the method described by Kemper and Rosenau
(1986).
75
2.3. Calculations and statistical analysis
Calculation of SOC contents on a per-hectare basis
used weighted averages for each sampling layer of the
volumetric SOC content of the 0±10 cm layer determined in 1997. Calculation of carbon application rate
involved the assumption that the water content of
wheat straw was 10% and that its carbon content
was 44%, i.e. Carbon (Residue/1.10) 0.44 (Lal,
1995). Stepwise linear regression analysis related total
%WSA to clay, silt and SOC content. Analysis of
variance (F-test) determined signi®cant residue or
tillage effects or interactions between tillage and
residue rates. Polynomial regression analysis was
employed to detect linear, quadratic or cubic relationships between residue rates and the dependent variables. Means of tillage treatments were compared
using Tukey's test.
3. Results
3.1. Soil organic carbon content
Measurements in 1996 indicated that seven years of
residue application had a positive effect on SOC
content in the 0±10 cm layer of the soil, but not in
the 10±30 cm depth (Fig. 1). Similar results were
reported by Dick et al. (1986b) and Havlin et al.
(1990). Some authors (Blevins et al., 1983; Dick
et al., 1986a; Angers et al., 1997) have reported higher
SOC levels at deeper depths under conventional tillage
Fig. 1. Residue rate effects on SOC at different depths after seven
years of residue application.
76
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Table 1
Tillage and residue rate effects on SOC (g kgÿ1) at 0±10 cm depth, 1996 data
Tillage
Residue rate (Mg haÿ1 yearÿ1)
0
2
4
8
16
significance
Ridge till
Plow till
No-till
Significancec
9.4
8.3
9.1
ns
11.1
10.3
11.5
ns
10.7
9.9
10.3
ns
14.1
11.2
13.3
ns
14.9
11.5
15.4
ns
La
La
Lb
a
Significant at p 0.05 level, L linear.
Significant at p 0.001 level, L linear.
c
Comparison of means using Tukey's test (p 0.05); ns not significant.
b
at the 10±20 cm depth compared with no-till. Climatic
factors, drainage, texture, type and depth of soil tillage
may be among important factors responsible for differences among locations and experiments.
The most signi®cant relationship of residue application rate and SOC content at 0±10 cm depth was
linear for all three tillage treatments (Table 1). The
data indicated that, on a weight basis, the rate of SOC
increase with residue application was lower with plow
till then other tillage treatments, and the rate of SOC
increase with residue application was comparable in
ridge till and no-till treatments. The range of SOC
contents in the 0±10 cm layer varied from 7.5 to
18.6 g kgÿ1.
More detailed measurements of SOC content
made in 1997 in the 0±10 cm layer are presented in
Fig. 2. Analysis of variance indicated signi®cant
effects of tillage methods, residue application rate
and interactions between them. With plow till and
no-till, signi®cant linear relationships were observed
in the 0±5 cm layer. However, no signi®cant relationship was observed between residue application rates
and volumetric SOC content with ridge till. The
most signi®cant linear regression equations relating
SOC content in the top 0±10 cm depth to residue
application rates are presented in Fig. 3. A reasonable
linear relationship was observed for plow till and
no-till. No signi®cant relationship was observed
with ridge till, only the intercept was highly signi®cant. These regression equations indicate that the
rate of SOC sequestration for each Mg of residue
applied was more for no-till than for plow till. The
results obtained in 1997 are different from those
in 1996, partly because bulk density of no-till treatments (average 1.49 Mg mÿ3) was higher than that of
plow till and ridge till treatments (both 1.34 Mg mÿ3).
The different results for ridge till treatments remain
unexplained. For carbon sequestration purposes, however, preference should be given to the 1997 data
because sampling was more detailed and repeated
and because results are expressed on a volumetric
basis.
Results of this experiment are comparable with
reported SOC increases on a Typic Paleudalf (silt
loam) in Kentucky (Blevins et al., 1983), on a Mollic
Ochraqualf (silty clay loam) in northwest Ohio (Dick
et al., 1986a), on Typic Fragiudalfs (silt loam) in
Northeast Ohio (Dick et al., 1986b; Bajracharya
et al., 1998) and on an Aeric Aqualf in Ohio (Bajracharya et al., 1998). In these studies, SOC content in
the top 5±7.5 cm of the soil was higher with no-till
compared with plow till. Therefore, the results of the
present study can be extrapolated with reasonable
con®dence to determine effects of changes in soil
and crop residue management on carbon sequestration
in silt loams of the eastern Corn Belt.
To calculate the conversion ef®ciency of carbon
applied in the residue into SOC, conversion of residue
in the equations into carbon is necessary (see Section 2.3). Carbon can be obtained by dividing the
slope of the regression line by 0.4 giving the conversion ef®ciency of C applied into SOC. This needs to be
divided by the number of years of application (eight
years) to obtain the ef®ciency on an annual basis.
Following this procedure, the conversion ef®ciency
was 0% with ridge till, 8% with plow till and 10% with
no-till. Most studies ®nd conversion ef®ciencies in the
range of 14% to 21% (Rasmussen and Collins, 1991).
Low conversion ef®ciencies in this experiment may be
the result of a lack of nutrients necessary for decomposition, since no fertilizer was applied (Himes,
1998).
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
77
Fig. 2. Residue rate effects on SOC at different depths with three different tillage systems after eight years of crop residue application. Note:
L, linear, ns, not significant differences between mulch rate effects across one depth, p 0.1 (*), 0.05 (**) or 0.001 (***).
3.2. Water stable aggregation
The %WSA data for the 0±10 cm layer are presented in Table 2. There were no treatment effects on
%WSA for soil below the 10-cm depth (data not
shown). Even in the 0±10 cm layer, the data are
variable and differences often not statistically signi®cant. The range of %WSA was 30±60%, and that of
MWD 0.23±1.12 mm. There was a linear increasing
trend in %WSA with increase in residue rate for plow
till and ridge till treatments. In contrast, increase in
residue application with no-till produced no consistent
increase in %WSA. There were no signi®cant effects
of tillage methods on the observed %WSA (averaging
across all residue treatments: 41.4% for PT, 44.7% for
RT, and 47.1% for NT). The MWD increased linearly
with residue rate in ridge till treatments only. Average
MWD was 0.45 mm with plow till, 0.55 mm with
ridge till and 0.66 mm with no-till. The data show
that residue application had a small positive effect on
%WSA with plow till and ridge till, and on MWD only
with ridge till. Residue application had no effect on
%WSA with no-till.
Reports in the literature on the effect of residue on
WSA are also mixed. Skidmore et al. (1986) did not
observe a positive effect of residue incorporation on
%WSA in the top 5 cm of a Kansas silty clay loam. In
Denmark, Christensen (1986) reported an increase in
mass of dry aggregates of 1±20 mm after 11 years of
straw incorporation compared with that of no straw of
78
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Fig. 3. Regression equations of SOC vs. residue application rate
with three different tillage systems after eight years of residue
application.
a loamy sand, but no effect on aggregation of a sandy
clay loam. Unger (1997b) found no difference in
MWD of WSA between no-till and cultivated Torrertic Paleustolls in Texas. However, he observed that in
some cases the percentage of small aggregates was
larger in the no-till than in the plow till treatment. In a
study on a high clay Orthic Humic Gleysol in Canada,
Angers et al. (1993) observed a decrease in MWD of
WSA after four years of plow till compared with notill. Beare et al. (1994) reported that plow till reduced
the size of WSA compared with no-till on a welldrained sandy clay loam in Athens, Georgia. In their
study, tillage effects on WSA disappeared below the
5 cm depth, except that the stability index of large
aggregates (>2 mm) was higher in the 5±15 cm layer
of the no-till compared with the plow till treatments.
Multiple regression equations showing the in¯uence of clay, silt and SOC on WSA are presented in
Table 3. The SOC content was a determinant of
%WSA in the topsoil, but not in the subsoil. The
SOC, clay and silt contents explained only 50% of the
variation in %WSA. These results differ from those
reported by Chaney and Swift (1984) for the surface
layer of 26 soils in Britain. In their study, organic
matter content explained almost 100% of the variation
in MWD of WSA. However, they report soils with a
wide variation in SOC contents (0.25±5.8% SOC).
Unger (1997a) reported a highly signi®cant, positive
relationship between SOC and %WSA >0.25 mm.
However, Unger (1995) did not observe a positive
relationship between SOC and WSA, and attributed
this to the fact that differences between treatments
were small, while differences between soils were large
(Unger, 1997a). For a uniform Crosby silt loam of the
present study, there was a signi®cant effect of texture
on aggregation. However, the range of SOC contents
was limited, which may be an explanation of the lack
of differences in %WSA. The results of the present
and other studies also indicate a lack of understanding
of the factors determining aggregation. Biological
factors like micro- and macro-¯ora and fauna are
not included in most studies but may play a critical
role. Additionally, organic matter quality (e.g. lignin
and nitrogen concentrations) may also be an important
determinant of WSA.
3.3. Water retention characteristics
Statistical analyses of the data showed that water
retention of soil for 0±10 cm depth at some matric
suctions was signi®cantly in¯uenced by the residue
rate, but not by tillage treatments, and no consistent
79
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Table 2
Tillage and residue rate effects on water stable aggregation in top 0±10 cm depth
Till
Plow till
Residue
(Mg haÿ1 yearÿ1)
Significance
Total
%WSA
2±5
1±2
0.5±1
0.25±0.5
0
2
4
8
16
0.3
0.5
1.1
0.3
1.1
Ca
0.8
3.4
4.2
5.3
6.4
Lb
3.0
5.0
7.3
11.2
10.6
Lb
9.8
9.0
12.2
16.9
14.1
nsd
15.5
14.9
18.9
17.9
16.9
nsd
0.23
0.35
0.49
0.57
0.62
Lb
29.5
32.8
43.8
51.6
49.1
Lb
0
2
4
8
16
1.9
0.7
0.9
0.6
2.1
nsd
3.5
5.6
5.3
5.5
7.1
nsd
4.7
7.4
7.4
9.1
9.7
Lb
7.7
13.5
12.4
9.5
16.4
nsd
14.1
18.6
17.5
24.9
17.4
Qc
0.43
0.53
0.52
0.53
0.72
nsd
31.9
45.8
43.6
49.5
52.7
La
0
2
4
8
16
0.5
6.3
1.5
2.6
2.9
nsd
2.3
9.9
4.2
7.6
5.7
nsd
5.6
11.4
6.3
7.7
7.3
nsd
12.6
17.6
7.8
11.8
7.8
nsd
18.5
15.6
19.2
16.7
26.5
Lb
0.36
1.12
0.47
0.70
0.65
nsd
39.4
60.6
39.0
46.4
50.1
nsd
Significance
No-till
MWD
(mm)
5±8
Significance
Ridge till
%WSA (mm)
a
Significant at p 0.1 level, C cubic.
Significant at p 0.05 level, L linear.
c
Significant at p 0.001 level, Q quadratic.
d
ns not significant
b
interaction effects were observed between tillage and
residue rate. Below the 10-cm depth, however, no
consistent treatment effects on water retention were
observed (results not shown). Soil water retention
increased with increasing residue rate for soil water
suction >30 kPa for depths of 0±10 cm (Table 4).
Using the relationship 2
/gr (where
is the
matric suction,
the surface tension, the density of
water, g the acceleration due to gravity and r the radius
of largest pores still ®lled with water), the water
Table 3
Stepwise regression analysis of WSA vs. clay, silt and SOC content
Depth (cm)
Regression equation
r
0±30
WSA 0.306 0.0039 clay
WSA ÿ0.688 0.016 clay 0.013 silt
WSA ÿ0.852 0.126 SOC 0.018 clay 0.013 silt
0.26
0.59
0.57
0±10
WSA 0.151 0.267 SOC
WSA ÿ0.058 0.260 SOC 0.005 silt
WSA ÿ1.039 0.296 SOC 0.015 clay 0.015 silt
0.50
0.57
0.68
10±30
WSA 0.219 0.0060 clay
WSA ÿ0.863 0.0192 clay 0.014 silt
WSA ÿ0.823 ÿ 0.069 SOC 0.019 clay 0.015 silt
0.40
0.65
0.66
Note: WSA is expressed as a fraction in these equations, not a percentage. The other parameters (clay, silt, SOC, are in percent).
80
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Table 4
Residue effects on soil water content (volume %) for 0±10 cm depth
Suction (kPa)
0
0.01
3
6
30
100
300
Mulch rate (Mg haÿ1 yearÿ1)
0
2
4
8
16
significance
45.25
43.94
42.70
43.02
28.55
26.03
23.83
43.19
42.69
41.65
40.46
30.09
28.92
27.06
43.72
41.53
40.17
39.67
30.09
28.03
26.18
45.15
41.99
40.60
39.84
31.25
29.33
28.55
45.45
42.82
41.89
41.00
33.57
31.66
30.03
nsc
Qa
Qa
nsc
Lb
Lb
Lb
a
Significant at p 0.05 level, Q quadratic.
Significant at p 0.001 level, L linear.
c
ns not significant.
b
retention curve can be used to assess pore size distribution. At 208C, the relationship becomes: r 0.15/
(where both,
and r are in cm; Marshall and
Holmes, 1979). The higher water content at suction
ranges from 30 to 300 KPa indicates that residue
application increases the amount of macropores with
diameters from 1 to 10 mm. Increased macroporosity
is a result of higher SOC content and possibly of
higher microbial and earthworm activity.
4. Conclusions
A linear relationship was observed between the
residue application rate and volumetric SOC content
for plow till and no-till, but not for ridge till. The
conversion ef®ciency of residue carbon into SOC was
lower for plow till (8%) than for no-till (10%), con®rming the ®rst hypothesis that carbon sequestration
rates under no-till are higher than under plow till. The
SOC levels increased with residue level in both, no-till
and plow till, con®rming the second hypothesis. No
increases in SOC contents were observed for ridge till
(1997 measurements), the reasons for which remain
obscure. There was no increase in %WSA with residue
rate in case of no till, but a slight increase with the
other tillage treatments. Water retention was not signi®cantly different between tillage treatments, but
residue application rate had a positive effect on water
retention at matric suctions between 30 and 300 KPa,
indicating an increase in macropores (1±10 mm) due to
residue application. There was no increase in aggregation and porosity with residue application under no-
tillage compared with the other tillage treatments, thus
leading to rejection of the third hypothesis. There was
a positive effect of residue application on aggregation
in plow till and ridge till treatments and on porosity in
all treatments.
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Raton, FL, pp. 15±49.
Rasmussen, P.E., Collins, H.P., 1991. Long-term impacts of tillage,
fertilizer, and crop residue on soil organic matter in temperate
semiarid regions. In: Brady, N.C. (Ed.), Advances in Agronomy
45. Academic Press, New York, pp. 93±134.
Russell, E.W., 1973. Soil Conditions and Plant Growth, tenth ed.
Longman, London.
Skidmore, E.L., Layton, J.B., Armbrust, D.V., Hooker, M.L., 1986.
Soil physical properties as influenced by cropping and residue
management. Soil Sci. Soc. Am. J. 50, 415±419.
Unger, P.W., 1995. Soil organic matter and water stable aggregate
effects on water infiltration. Soil Sci. 3, 9±16.
Unger, P.W., 1997a. Aggregate and organic carbon concentration
interrelationships of a Torrertic Paleustoll. Soil Tillage Res. 42,
pp. 95±113.
Unger, P.W., 1997b. Management-induced aggregation and organic
carbon concentrations in the surface layer of a Torrertic
Paleustoll. Soil Tillage Res. 42, pp. 185±208.
Yoder, R.E., 1936. A direct method of aggregate analysis and a
study of the physical nature of erosion losses. J. Am. Soc.
Agron. 28, 337±351.
Crop residue and tillage effects on carbon
sequestration in a Luvisol in central Ohio
S.W. Duiker, R. Lal*
School of Natural Resources, Ohio State University, 2021 Coffey Road,Columbus, OH 43210-1085,USA
Received 3 July 1998; received in revised form 2 March 1999; accepted 1 June 1999
Abstract
Soils play a key role in the global carbon cycle. They can be a source or a sink of carbon and in¯uence CO2 concentrations in
the atmosphere. In order to calculate the carbon budget of a region, the effect of soil management practices on carbon
sequestration in soils needs to be quanti®ed. Objectives of this experiment were to determine: (i) the effects of ridge till, plow
till and no-till on the soil organic carbon (SOC) pool; (ii) the SOC loss or sequestration for mulch rates of 0±
16 Mg haÿ1 yearÿ1 wheat (Triticum aestivum L.) straw applied in combination with each tillage method, and (iii) impacts of
tillage and crop residue treatments on soil physical quality, including aggregation and porosity. The experiment was initiated
in 1989 on a Crosby silt loam (Stagnic Luvisol) in Central Ohio. Seven years after initiation of the experiment, there was a
positive, linear effect of residue application rate on SOC contents in all tillage treatments. In the eighth year of the experiment
these trends were con®rmed for plow and no-till, but not for ridge till. Linear-regression equations, relating SOC content for
the 0±10 cm soil depth to mulch rate, were: for no-till: SOC (Mg haÿ1) 15.21 0.32 [Residue (Mg haÿ1 yearÿ1)] (r 0.68)
and for plow till: SOC 11.95 0.27 [Residue] (p 0.72). The carbon conversion ef®ciencies were 8% per year for plow till
and 10% per year for no-till. Detailed sampling at different depths revealed that increases in SOC content were only signi®cant
for the 0±5 cm depths of plow and no-till treatments. Effects of crop residue application on water stable aggregation in the 0±
10 cm layer were most pronounced with plow till and ridge till but not with no-till. Water retention characteristics, a measure
of pore size distribution, was not in¯uenced by tillage system, but crop residue application had a signi®cant effect on water
retention in the 0±10 cm layer at matric suctions of 30±300 kPa. This means that residue application increased macropores of
diameters 1±10 mm. It is concluded that, depending on the amount of crop residue returned to the soil, the large numbers
of farmers converting from plow to no-till cultivation in the Corn Belt may create an important sink for atmospheric CO2.
# 1999 Elsevier Science B.V. All rights reserved.
Keywords: Soil organic matter; Aggregation; Carbon sequestration; Mulching; Conservation tillage; Greenhouse effect; Soil quality
1. Introduction
*Corresponding author. Tel.: +1-614-292-9069; fax: +1-614292-7432
E-mail address: [email protected] (R. Lal)
Concern with global warming has led to a surge of
interest in evaluating the effect of management practices on carbon sequestration in soils. This interest is
justi®ed because soils play a key role in the global
0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 5 9 - 8
74
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
carbon budget, containing 3.5% of the carbon reserves
of the earth, compared with 1.7% in the atmosphere,
8.9% in fossil fuels, 1.0% in biota and 84.9% in the
oceans (Lal et al., 1995). Land use change is still a
major source of carbon emission due to burning and
decomposition of vegetation and declining soil
organic carbon (SOC) contents in soils. Depending
on management, soils can be an important sink for
carbon. However, realization of the sink capacity of
soils requires adoption of appropriate soil management practices that increase SOC content.
In the U.S., many farmers have shifted from plow
till to conservation tillage systems. The area under
conservation tillage (leaving >30% of crop residue on
the soil surface) has increased from 29 million ha
(26% of planted area) in 1989 to 40 million ha
(35%) in 1994 (Bull and Sandretto, 1996), and is
expected to increase to 75% by the year 2020 (Lal,
1997). The Corn Belt and Northern Plains are the
regions where conservation tillage (especially no-till)
is most popular. In 1994, about 14 million ha of
cropland in the Corn Belt had >30% residue coverage,
while 17 million ha had 0.25 mm and mean
weight diameter (MWD) were calculated according
to the method described by Kemper and Rosenau
(1986).
75
2.3. Calculations and statistical analysis
Calculation of SOC contents on a per-hectare basis
used weighted averages for each sampling layer of the
volumetric SOC content of the 0±10 cm layer determined in 1997. Calculation of carbon application rate
involved the assumption that the water content of
wheat straw was 10% and that its carbon content
was 44%, i.e. Carbon (Residue/1.10) 0.44 (Lal,
1995). Stepwise linear regression analysis related total
%WSA to clay, silt and SOC content. Analysis of
variance (F-test) determined signi®cant residue or
tillage effects or interactions between tillage and
residue rates. Polynomial regression analysis was
employed to detect linear, quadratic or cubic relationships between residue rates and the dependent variables. Means of tillage treatments were compared
using Tukey's test.
3. Results
3.1. Soil organic carbon content
Measurements in 1996 indicated that seven years of
residue application had a positive effect on SOC
content in the 0±10 cm layer of the soil, but not in
the 10±30 cm depth (Fig. 1). Similar results were
reported by Dick et al. (1986b) and Havlin et al.
(1990). Some authors (Blevins et al., 1983; Dick
et al., 1986a; Angers et al., 1997) have reported higher
SOC levels at deeper depths under conventional tillage
Fig. 1. Residue rate effects on SOC at different depths after seven
years of residue application.
76
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Table 1
Tillage and residue rate effects on SOC (g kgÿ1) at 0±10 cm depth, 1996 data
Tillage
Residue rate (Mg haÿ1 yearÿ1)
0
2
4
8
16
significance
Ridge till
Plow till
No-till
Significancec
9.4
8.3
9.1
ns
11.1
10.3
11.5
ns
10.7
9.9
10.3
ns
14.1
11.2
13.3
ns
14.9
11.5
15.4
ns
La
La
Lb
a
Significant at p 0.05 level, L linear.
Significant at p 0.001 level, L linear.
c
Comparison of means using Tukey's test (p 0.05); ns not significant.
b
at the 10±20 cm depth compared with no-till. Climatic
factors, drainage, texture, type and depth of soil tillage
may be among important factors responsible for differences among locations and experiments.
The most signi®cant relationship of residue application rate and SOC content at 0±10 cm depth was
linear for all three tillage treatments (Table 1). The
data indicated that, on a weight basis, the rate of SOC
increase with residue application was lower with plow
till then other tillage treatments, and the rate of SOC
increase with residue application was comparable in
ridge till and no-till treatments. The range of SOC
contents in the 0±10 cm layer varied from 7.5 to
18.6 g kgÿ1.
More detailed measurements of SOC content
made in 1997 in the 0±10 cm layer are presented in
Fig. 2. Analysis of variance indicated signi®cant
effects of tillage methods, residue application rate
and interactions between them. With plow till and
no-till, signi®cant linear relationships were observed
in the 0±5 cm layer. However, no signi®cant relationship was observed between residue application rates
and volumetric SOC content with ridge till. The
most signi®cant linear regression equations relating
SOC content in the top 0±10 cm depth to residue
application rates are presented in Fig. 3. A reasonable
linear relationship was observed for plow till and
no-till. No signi®cant relationship was observed
with ridge till, only the intercept was highly signi®cant. These regression equations indicate that the
rate of SOC sequestration for each Mg of residue
applied was more for no-till than for plow till. The
results obtained in 1997 are different from those
in 1996, partly because bulk density of no-till treatments (average 1.49 Mg mÿ3) was higher than that of
plow till and ridge till treatments (both 1.34 Mg mÿ3).
The different results for ridge till treatments remain
unexplained. For carbon sequestration purposes, however, preference should be given to the 1997 data
because sampling was more detailed and repeated
and because results are expressed on a volumetric
basis.
Results of this experiment are comparable with
reported SOC increases on a Typic Paleudalf (silt
loam) in Kentucky (Blevins et al., 1983), on a Mollic
Ochraqualf (silty clay loam) in northwest Ohio (Dick
et al., 1986a), on Typic Fragiudalfs (silt loam) in
Northeast Ohio (Dick et al., 1986b; Bajracharya
et al., 1998) and on an Aeric Aqualf in Ohio (Bajracharya et al., 1998). In these studies, SOC content in
the top 5±7.5 cm of the soil was higher with no-till
compared with plow till. Therefore, the results of the
present study can be extrapolated with reasonable
con®dence to determine effects of changes in soil
and crop residue management on carbon sequestration
in silt loams of the eastern Corn Belt.
To calculate the conversion ef®ciency of carbon
applied in the residue into SOC, conversion of residue
in the equations into carbon is necessary (see Section 2.3). Carbon can be obtained by dividing the
slope of the regression line by 0.4 giving the conversion ef®ciency of C applied into SOC. This needs to be
divided by the number of years of application (eight
years) to obtain the ef®ciency on an annual basis.
Following this procedure, the conversion ef®ciency
was 0% with ridge till, 8% with plow till and 10% with
no-till. Most studies ®nd conversion ef®ciencies in the
range of 14% to 21% (Rasmussen and Collins, 1991).
Low conversion ef®ciencies in this experiment may be
the result of a lack of nutrients necessary for decomposition, since no fertilizer was applied (Himes,
1998).
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
77
Fig. 2. Residue rate effects on SOC at different depths with three different tillage systems after eight years of crop residue application. Note:
L, linear, ns, not significant differences between mulch rate effects across one depth, p 0.1 (*), 0.05 (**) or 0.001 (***).
3.2. Water stable aggregation
The %WSA data for the 0±10 cm layer are presented in Table 2. There were no treatment effects on
%WSA for soil below the 10-cm depth (data not
shown). Even in the 0±10 cm layer, the data are
variable and differences often not statistically signi®cant. The range of %WSA was 30±60%, and that of
MWD 0.23±1.12 mm. There was a linear increasing
trend in %WSA with increase in residue rate for plow
till and ridge till treatments. In contrast, increase in
residue application with no-till produced no consistent
increase in %WSA. There were no signi®cant effects
of tillage methods on the observed %WSA (averaging
across all residue treatments: 41.4% for PT, 44.7% for
RT, and 47.1% for NT). The MWD increased linearly
with residue rate in ridge till treatments only. Average
MWD was 0.45 mm with plow till, 0.55 mm with
ridge till and 0.66 mm with no-till. The data show
that residue application had a small positive effect on
%WSA with plow till and ridge till, and on MWD only
with ridge till. Residue application had no effect on
%WSA with no-till.
Reports in the literature on the effect of residue on
WSA are also mixed. Skidmore et al. (1986) did not
observe a positive effect of residue incorporation on
%WSA in the top 5 cm of a Kansas silty clay loam. In
Denmark, Christensen (1986) reported an increase in
mass of dry aggregates of 1±20 mm after 11 years of
straw incorporation compared with that of no straw of
78
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Fig. 3. Regression equations of SOC vs. residue application rate
with three different tillage systems after eight years of residue
application.
a loamy sand, but no effect on aggregation of a sandy
clay loam. Unger (1997b) found no difference in
MWD of WSA between no-till and cultivated Torrertic Paleustolls in Texas. However, he observed that in
some cases the percentage of small aggregates was
larger in the no-till than in the plow till treatment. In a
study on a high clay Orthic Humic Gleysol in Canada,
Angers et al. (1993) observed a decrease in MWD of
WSA after four years of plow till compared with notill. Beare et al. (1994) reported that plow till reduced
the size of WSA compared with no-till on a welldrained sandy clay loam in Athens, Georgia. In their
study, tillage effects on WSA disappeared below the
5 cm depth, except that the stability index of large
aggregates (>2 mm) was higher in the 5±15 cm layer
of the no-till compared with the plow till treatments.
Multiple regression equations showing the in¯uence of clay, silt and SOC on WSA are presented in
Table 3. The SOC content was a determinant of
%WSA in the topsoil, but not in the subsoil. The
SOC, clay and silt contents explained only 50% of the
variation in %WSA. These results differ from those
reported by Chaney and Swift (1984) for the surface
layer of 26 soils in Britain. In their study, organic
matter content explained almost 100% of the variation
in MWD of WSA. However, they report soils with a
wide variation in SOC contents (0.25±5.8% SOC).
Unger (1997a) reported a highly signi®cant, positive
relationship between SOC and %WSA >0.25 mm.
However, Unger (1995) did not observe a positive
relationship between SOC and WSA, and attributed
this to the fact that differences between treatments
were small, while differences between soils were large
(Unger, 1997a). For a uniform Crosby silt loam of the
present study, there was a signi®cant effect of texture
on aggregation. However, the range of SOC contents
was limited, which may be an explanation of the lack
of differences in %WSA. The results of the present
and other studies also indicate a lack of understanding
of the factors determining aggregation. Biological
factors like micro- and macro-¯ora and fauna are
not included in most studies but may play a critical
role. Additionally, organic matter quality (e.g. lignin
and nitrogen concentrations) may also be an important
determinant of WSA.
3.3. Water retention characteristics
Statistical analyses of the data showed that water
retention of soil for 0±10 cm depth at some matric
suctions was signi®cantly in¯uenced by the residue
rate, but not by tillage treatments, and no consistent
79
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Table 2
Tillage and residue rate effects on water stable aggregation in top 0±10 cm depth
Till
Plow till
Residue
(Mg haÿ1 yearÿ1)
Significance
Total
%WSA
2±5
1±2
0.5±1
0.25±0.5
0
2
4
8
16
0.3
0.5
1.1
0.3
1.1
Ca
0.8
3.4
4.2
5.3
6.4
Lb
3.0
5.0
7.3
11.2
10.6
Lb
9.8
9.0
12.2
16.9
14.1
nsd
15.5
14.9
18.9
17.9
16.9
nsd
0.23
0.35
0.49
0.57
0.62
Lb
29.5
32.8
43.8
51.6
49.1
Lb
0
2
4
8
16
1.9
0.7
0.9
0.6
2.1
nsd
3.5
5.6
5.3
5.5
7.1
nsd
4.7
7.4
7.4
9.1
9.7
Lb
7.7
13.5
12.4
9.5
16.4
nsd
14.1
18.6
17.5
24.9
17.4
Qc
0.43
0.53
0.52
0.53
0.72
nsd
31.9
45.8
43.6
49.5
52.7
La
0
2
4
8
16
0.5
6.3
1.5
2.6
2.9
nsd
2.3
9.9
4.2
7.6
5.7
nsd
5.6
11.4
6.3
7.7
7.3
nsd
12.6
17.6
7.8
11.8
7.8
nsd
18.5
15.6
19.2
16.7
26.5
Lb
0.36
1.12
0.47
0.70
0.65
nsd
39.4
60.6
39.0
46.4
50.1
nsd
Significance
No-till
MWD
(mm)
5±8
Significance
Ridge till
%WSA (mm)
a
Significant at p 0.1 level, C cubic.
Significant at p 0.05 level, L linear.
c
Significant at p 0.001 level, Q quadratic.
d
ns not significant
b
interaction effects were observed between tillage and
residue rate. Below the 10-cm depth, however, no
consistent treatment effects on water retention were
observed (results not shown). Soil water retention
increased with increasing residue rate for soil water
suction >30 kPa for depths of 0±10 cm (Table 4).
Using the relationship 2
/gr (where
is the
matric suction,
the surface tension, the density of
water, g the acceleration due to gravity and r the radius
of largest pores still ®lled with water), the water
Table 3
Stepwise regression analysis of WSA vs. clay, silt and SOC content
Depth (cm)
Regression equation
r
0±30
WSA 0.306 0.0039 clay
WSA ÿ0.688 0.016 clay 0.013 silt
WSA ÿ0.852 0.126 SOC 0.018 clay 0.013 silt
0.26
0.59
0.57
0±10
WSA 0.151 0.267 SOC
WSA ÿ0.058 0.260 SOC 0.005 silt
WSA ÿ1.039 0.296 SOC 0.015 clay 0.015 silt
0.50
0.57
0.68
10±30
WSA 0.219 0.0060 clay
WSA ÿ0.863 0.0192 clay 0.014 silt
WSA ÿ0.823 ÿ 0.069 SOC 0.019 clay 0.015 silt
0.40
0.65
0.66
Note: WSA is expressed as a fraction in these equations, not a percentage. The other parameters (clay, silt, SOC, are in percent).
80
S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81
Table 4
Residue effects on soil water content (volume %) for 0±10 cm depth
Suction (kPa)
0
0.01
3
6
30
100
300
Mulch rate (Mg haÿ1 yearÿ1)
0
2
4
8
16
significance
45.25
43.94
42.70
43.02
28.55
26.03
23.83
43.19
42.69
41.65
40.46
30.09
28.92
27.06
43.72
41.53
40.17
39.67
30.09
28.03
26.18
45.15
41.99
40.60
39.84
31.25
29.33
28.55
45.45
42.82
41.89
41.00
33.57
31.66
30.03
nsc
Qa
Qa
nsc
Lb
Lb
Lb
a
Significant at p 0.05 level, Q quadratic.
Significant at p 0.001 level, L linear.
c
ns not significant.
b
retention curve can be used to assess pore size distribution. At 208C, the relationship becomes: r 0.15/
(where both,
and r are in cm; Marshall and
Holmes, 1979). The higher water content at suction
ranges from 30 to 300 KPa indicates that residue
application increases the amount of macropores with
diameters from 1 to 10 mm. Increased macroporosity
is a result of higher SOC content and possibly of
higher microbial and earthworm activity.
4. Conclusions
A linear relationship was observed between the
residue application rate and volumetric SOC content
for plow till and no-till, but not for ridge till. The
conversion ef®ciency of residue carbon into SOC was
lower for plow till (8%) than for no-till (10%), con®rming the ®rst hypothesis that carbon sequestration
rates under no-till are higher than under plow till. The
SOC levels increased with residue level in both, no-till
and plow till, con®rming the second hypothesis. No
increases in SOC contents were observed for ridge till
(1997 measurements), the reasons for which remain
obscure. There was no increase in %WSA with residue
rate in case of no till, but a slight increase with the
other tillage treatments. Water retention was not signi®cantly different between tillage treatments, but
residue application rate had a positive effect on water
retention at matric suctions between 30 and 300 KPa,
indicating an increase in macropores (1±10 mm) due to
residue application. There was no increase in aggregation and porosity with residue application under no-
tillage compared with the other tillage treatments, thus
leading to rejection of the third hypothesis. There was
a positive effect of residue application on aggregation
in plow till and ridge till treatments and on porosity in
all treatments.
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